This is a bit funny actually. I just started creating something in the HPL Editor, and slowly but surely ended up with what I have below. Right now I do not have a story at all, I have got ideas for what i could do with it, but I would like to hear what people think of what I have made so far. I can keep updating this Post with future screenshots showcasing the custom story as it is developed.

I am hoping to get most of it done till Amnesia: A Machine For Pigs, therefore I can finish the outdoor environments.

I know that this is because it's a WIP, but don't forget to add a skybox, and ground texture to the map! Also, as Robo said, you can add a bit of detail to spice it up.

If you're really confident in your abilities, you could even try tearing down the "symmetrical-feel" of the map by adding intense changes to either the left, or right side of the building. Of course if you're going for a "refined, and/or organized" feel for your building, I don't recommend you try this.

Yeah, I'm just doing detailing ATM so i haven't laid the flooring for the garden out front yet. I like to idea of changes to the symmetrical feel, but I don't know if it would change the effect of what it looks like... Not sure really. Even less sure of what i could add/change Lol.

You could add some "broken parts", then use wooden beams to create scaffolds with ropes (+ other details) hanging from them - as if there was a construction work going on which was aborted. I'd also exaggerate the lighting from the windows, give it billboards etc.

I thank you so much for everyone's input, I was at work today So i replied above whilst there.
I took in everyone's advice, and I and I added tree's and the foggy look to it, I wasn't so sure of what an effect it has on the castle itself. And i was pleasantly surprised.